Cupola slag

Cupola slag consists of 30 % refractory material, 10 % sand (from internal scrap), 40 % CaO (flux), 10 % cokes ashes, and 10 % bum-off material. 

An important aspect of cupola slag is its high Si02-content. After quenching, the slag has a vitrified stmcture. This generates an inert non-leaching material. 

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Table 3.8 Typical cupola slag composition [172, Neumann, 1994], [156, Godinot, 2001]...

Air-cooled cupola slag Crushing - generation of glassy dust - handling requirements due to glassy nature... 

Basalt (electric furnace) Basalt + limestone (cupola) Slag Wool (cupola)... 

Carbon brick and block ate used to line the cupola well (73) or cmcible. When properly installed and cooled carbon linings last for many months or even years of intermittent operation. Their resistance to molten iron and both acid and basic slags provides not only insurance against breakouts but also operational flexibility to produce different iron grades without the necessity of changing refractories. Carbon is also widely used for the tap hole blocks, breast blocks, slagging troughs, and dams. 

FLUX (Slag). A material added to the contents of a smelting furnace or a cupola for the purpose of purging the metal of impurities, and or rendering the slag more liquid. The flux most commonly used in iron and steel furnaces is limestone, which is charged in the proper proportions with the iron and fuel. The slag is a liquid mixture of ash. Ilux. and other impurities. 

Water-cooled cupola furnaces several meters high and with shafts up to 1 m wide are used for the manufacture of rock and slag fibers. The raw materials are added alternately with coke. Metallic iron is formed from the iron-containing raw material and has to be regularly drawn off. 

In lead smelting, the oxygen-enriched blast has been used in lead cupola and slag fuming furnaces. Oxygen enrichment of the copper blast furnace is also common. 

The cupola furnace has the specific feature that the lining material (quartz-clay mixture) of the furnace at the melting zone only lasts for one melting campaign. The main part of the refractory is converted into slag. The amount to be taken out and disposed of as waste is much smaller than the applied amount. 

A flux is used to render the slag fluid enough to separate from the iron and to allow it to flow freely from the cupola. The most commonly used flux is limestone (calcium carbonate), which calcines in the cupola shaft to form lime, a basic oxide, which then combines with the other slag-forming constituents (mainly acidic in character) to provide a fluid slag. 

Most cupolas operate with an acidic or slightly basic slag (basicity <1.2). Basic cupolas (basicity up to 2) offer 3 advantages higher carbon lower sulphur... 

For acidic cupolas, dry filters can be used. The slag of basic cupolas has a higher melting point. So a flux based on Cap2 is generally used to maJce it fluid. In this type of cupola, there are emissions of fluor-containing components. This necessitates the application of wet scmbbers for efficient capture of these components. 

This technique applies to all new and existing cupola installations. If basic slag is used, a wet dedusting is necessary. 

Injection into the well Oxygen is injected into the coke bed from a ring-main which supplies water-cooled injectors, whose number depends on the cupola size. Oxygen used in this way is at least twice as effective as when it is used to enrich the blast supply directly. However, this t5q)e of injection is confined to continuously-tapped cupolas, since with intermittent tapping there is a risk that slag and or metal may rise to the level of the injectors. The technique was developed in the UK but it has not found widespread application... 

Replacement of a cupola by an induction or rotary furnace results in a reduction in the direct emissions of CO and SO2 and a reduced amount of slag. Induction furnaces show a reduced emission of NOx and a lower risk of dioxin formation. The indirect emissions generated by the use of induction furnaces, depend on the local electricity generation infrastructure. 

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